Articulation marks always render above the notehead in Gradus, regardless of stem direction — a confirmed bug, not a rendering-library question

Default: an articulation mark (staccato dot, accent, tenuto, marcato, fermata, staccatissimo) is placed on the notehead side opposite the stem — below for a stem-up note, above for a stem-down note. Exception: when the notehead is outside the staff, the mark sits toward the staff regardless of stem direction.

Gould, Behind Bars, Articulation chapter (opposite-stem default and the outside-the-staff exception stated explicitly).

This rule can be decided from pitches, durations and voices — no layout required. A validator can check it before anything is drawn.